The invention relates to porcelain enamel coatings, and particularly, to water-resistant porcelain enamel coatings for use in water heaters.
Porcelain enamel is subject to corrosion and dissolution by hot water. This can cause difficulties in applications such as hot water heaters. In a water heater, once the porcelain enamel coating protecting a metal substrate is dissolved through to the substrate, then the substrate corrodes rapidly and is perforated through. At this point the water heater must be replaced.
Attempts to improve the corrosion resistance of porcelain enamel have resulted in the use of various mill additions. However, mill additions that improve corrosion resistance tend to result in porcelain enamels that are subject to fish scaling or crazing.
Therefore, it would be desirable to have an improved porcelain enamel coating which is not only highly water-resistant, but also resists crazing or cracking.
It has been found that the use of mill additions containing a combination of zirconia compounds and silica improves the corrosion resistance of the porcelain enamel to hot water. In addition to good corrosion resistance, the coating adheres well to the metal substrate.
The invention provides a method of manufacturing a water-resistant porcelain enamel coating. The method comprises providing a ground glass; adding mill additions including silica and a zirconia compound to form a mixture; applying the mixture to a substrate; and firing the coated substrate to form the porcelain enamel coating. The resulting coating has good water-resistance properties, good adhesion to the substrate, and minimal cracking. Therefore, this coating is useful, for example, to increase the life of water heaters.
The invention also provides a porcelain enamel coating prepared by the above process, and a water heater coated with the porcelain enamel.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description and claims.
In one aspect, the invention provides a method of manufacturing water-resistant porcelain enamel coating. The method comprises providing ground glass and adding mill additions to the ground glass to form a mixture, wherein the mill additions comprise silica and a zirconia compound. The mixture is applied to a metal substrate to form a coated substrate, and the coated substrate is fired to form the water-resistant porcelain enamel coating. The silica and zirconia compound mill additions may comprise at least about 25 and less than about 70 parts by weight per hundred parts by weight ground glass.
In another aspect, the invention provides a method of manufacturing a water-resistant porcelain enamel coating suitable for use on a water heater. The method comprises providing a ground borosilicate glass, and adding mill additions to the ground glass to form a mixture. The mill additions comprise (a) a zirconia compound constituting at least about 10 parts by weight per hundred parts by weight ground glass and (b) a silica compound. The mixture is applied to a water heater and the water heater is fired at a temperature of about 1000xc2x0 F. to about 1700xc2x0 F. to form the water-resistant porcelain enamel coating.
In yet a further aspect, the invention provides a method of manufacturing a water-resistant porcelain enamel coating. The method comprises providing ground glass, and adding mill additions to the ground glass to form a mixture. The mill additions comprise silica and a zirconia compound and the mixture comprises at least about 15 parts and less than about 60 parts by weight of the silica mill addition per hundred parts by weight of the ground glass. The method further comprises applying the mixture to a metal substrate to form a coated substrate, and firing the coated substrate at a temperature of about 1000 to 1700xc2x0 F.(538-927xc2x0 C.) to form the water-resistant porcelain enamel coating.
In another aspect, the invention provides a method of manufacturing a water-resistant porcelain enamel coating. The method comprises providing ground glass and adding mill additions to the ground glass to form a mixture. The mill additions comprise a zirconia compound including particles having a median particle size of less than about 10 microns. The mixture is applied to a metal substrate to form a coated substrate and the coated substrate is fired to form the water-resistant porcelain enamel coating. The substrate may a water heater.
In a further aspect, the invention provides a method of manufacturing a water-resistant porcelain enamel coating. The method comprises providing ground glass, and adding mill additions to the ground glass to form a mixture. The mill additions comprise a zirconia compound. The method further comprises applying the mixture to a metal substrate to form a coated substrate, and firing the coated substrate to form the water-resistant porcelain enamel coating. The zirconia compound mill additions may comprise at least about 10 and less than about 120 parts by weight per hundred parts by weight ground glass. The substrate may be a water heater.